Injection molding of parts made of thermoplastic material generally has three main phases: first, injection of material into a mold; second, packing and cooling of the material in the mold in forming the desired part, and third, ejection of the molded part from the mold. The molding cycle time is commonly referred to as the duration of time from the start of the injection phase to initiation of the ejection phase.
Ability to accurately predict molding cycle time is of paramount importance in injection molding, particularly since it relates directly to the production rate and part quality. When cycle time exceeds a desired range, the production rate is compromised. In some instances, the part may exhibit brittle failure during ejection due to excessively increased friction force. In addition, ejector pins can be damaged due to the friction force exceeding the maximum ejection force that can be withstood by the ejectors. Further, if the part is ejected prematurely when only a thin layer of polymer is solidified, ejection may cause permanent deformation leading to surface defects. For most injection molders, cycle time is estimated through molding trials which are costly and time consuming. It is even more difficult to determine a proper cycle time range for new materials due to lack of knowledge of the material behavior.
Production tooling for the injection molding process is very costly to build. Capital cost is linearly proportional to the cycle time; therefore, cycle time minimization is critical in product cost reduction. Modeling software can be used to optimize the molding process in the early design phase. Modeling software calculates temperatures, velocities, viscosities, shear rates, and pressures as a function of time. However, the cycle time prediction is still left for users to predict.
Consequently, a need exists for an innovation which will provide an effective approach to predicting an injection molding target cycle time that can be used to determine an optimal cycle time for an injection molded part.